This invention relates to a utility knife comprising an elongate handle, formed by two elongate handle portions, and a blade carrier assembly, wherein the two handle portions are held together by mutually interlocking and overlapping nose portions and by a releasable locking structure.
In the field of utility knives, many different arrangements have been proposed for securing two mating handle halves to one another. One alternative for providing a simple mating of utility knife handle portions has been to provide a forwardly projecting tab at the forward end of one of the handle portions and a slot formed in the forward end of the other of the handle portions. The tab of one handle portion is inserted into the slot of the other handle portion, and the rearward portions of the handle portions are then releasably secured to one another.
It has been found that the tab and slot type of connecting arrangement has been beneficial in preventing a splaying of the handle portions away from one another when a bending or twisting force is applied to an extended knife blade during particularly demanding applications. This is primarily due to the fact that the connection between the handle portions in this type of tab and slot arrangement exists towards the very front end of the knife blade, where the large separating forces are primarily encountered.
As another alternative, commonly-assigned U.S. Pat. No. 5,121,544, having the same inventor as the present application, describes a utility knife comprising an elongate handle that can be assembled and disassembled without the need for additional tools. The handle is assembled by sliding the mating handle portions relatively longitudinally of one another until a latch part near the rear end of one handle portion snaps into latching-engagement with the front edge of an aperture formed in the other handle portion. Extending flank portions formed on each of the handle portions cooperate and overlie each other so as to interlock between the forward portions of the respective handle portions. Another similar interlock arrangement is disclosed in U.S. Pat. No. 5,005,290, also having common inventorship with the present application. It is known that the interlock arrangement is advantageous for its ease of assembly. In the ""290 patent, the interlock also serves to grip the blade between the handle portions by also including a wedging surface on each of the interlocking members. The disclosure of U.S. Pat. Nos. 5,121,544 and 5,005,290 are hereby incorporated by reference.
Heretofore, the xe2x80x9cwedge lockxe2x80x9d type arrangement and the tab and slot arrangement have been considered to be mutually exclusive ways of connecting utility knife handle members, as there has been no recognized need or motivation to combine the two.
While many utility knife handles are made from metal to provide a robust, long life product, plastic is the material of choice from a manufacturing cost perspective. However, the Applicant has found that, with age, plastic handles employing the tab and slot arrangement may be vulnerable to breakage (particularly at a thin portion of plastic forming the slot) when it is subject to high levels of stress when the knife blade has a torsional or bending load applied thereto. In addition, because this type of connection is at the very front end of the handle, it is subject to direct impact if the utility knife is dropped.
To obviate this problem, the obvious solution to one skilled in the art would have been to reinforce the front end of the knife handle, for example, by using a metal insert or by using a larger plastic portion to form the slot. However, in accordance with the present invention, the Applicant has derived the unobvious solution by providing a plastic utility knife handle that employs a combination tab/slot and wedge lock connection, without modifying or rigidifying the tab/slot connection. This arrangement maintains the handle portions in connected relation in the event that the tab/slot arrangement should fail. Moreover, it has been found that the resistance to the splaying forces is more evenly distributed along the length of the knife handle such stresses are not concentrated. This reduces splaying or separation of the handle members during use, while also increasing the resistance to breakage by distributing the splaying forces.
In accordance with the present invention, there is provided a utility knife having an elongated handle with a front end and a rear end. The handle defines a cavity therein and includes carrier guide structure provided within the cavity. The elongated handle comprises a first plastic handle portion and a mating second plastic handle portion, each having front and rear ends corresponding to the front and rear ends of the elongated handle. Releasable locking structure is associated with the first handle portion and the second handle portion for releasably locking the first handle structure to the second handle structure. A blade carrier assembly is constructed and arranged to carry a knife blade and to be manually slidable on the carrier guide structure in a longitudinal direction with respect to the handle to selectively extend the knife blade outwardly from the front end of the handle or retract the knife blade into the cavity. The first handle portion comprises first interlock structure, including forwardly-extending first projections and a rearwardly-extending first recesses, and a projecting tab proximate the front end of the first handle portion and extending toward the front end of the first handle portion. The second handle portion comprises second interlock structure, including rearwardly-extending second projections and forwardly-extending second recesses, and a longitudinal slot proximate the front end of the second handle portion. The first and second handle portions are constructed and arranged to be cooperatively mated with one another to form the elongated handle by longitudinally displacing the first handle portion relative to the second handle portion so that (i) the first projections of the first interlock structure operatively engage with the second recesses of the second interlock structure, (ii) the second projections of the second interlock structure operatively engage with the first recesses of the first interlock structure, and (iii) the projecting tab of the first handle portion extends forwardly into the longitudinal slot formed in the front end of the second handle portion. An inside surface of the projecting tab and an opposed interior surface of the slot formed in the front end of the second handle portion define an opening in the front end of the handle through which the blade can be extended and retracted. The releasable locking structure prevents longitudinal displacement of the first handle portion relative to the second handle portion thereby preventing separation of the first handle portion from the second handle portion. The releasable locking structure is releasable to enable the first and second handle portions to be longitudinally displaceable relative to one another to enable (i) the first projections to be longitudinally moved out of the second recesses, (ii) the second projections to be longitudinally moved out of the first recesses, and (iii) the tab to be longitudinally moved out of the slot and thereby allow separation of the first and second handle portions.
Other objects, features, and characteristics of the present invention, as well as the methods of operation of the invention and the function and interrelation of the elements of structure, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this disclosure, wherein like reference numerals designate corresponding parts in the various figures.